The ryuu or dragon may be an imaginary flying creature, but in some Asian countries (namely Japan and China), it is believed that they have control over water and rain, and they are worshipped as kami. In Japan, kami that has control over water are known as ryuujin.

Eventually it became too difficult to keep a living horse for the sake of prayer so it evolved into wooden boards with the image of a horse on it (Ema). This also allowed something that was originally created by the Emperor to be spread to normal citizens as well, and now people offer these wooden boards to pray for their various wishes.